Jet engine combustion processes



Sept. 25, 1962 4 Sheets-Sheet 1 Filed Feb. 9, 1959 COMPOSITION OF COOLANT WEIGHT 2 25 /0 ETHYL. ALCOHOL; 75% WATER.

4 25% |,4 DIOXANE; 75% WATER.

5 25% PROPYLENE OXIDE; 75% WATER.

COOLANT -AIR WEIGHT RATIO OJO FIG. 3

CHAMBER ME UL v HZ 0 EN 3 m 2 M E m 3 I U T N 21 m 5 1 T S U B M O L C l E 2 l R w 2 O VIVL S s E R P m 2 M VAT O c 7 m m L m 0 m l A INVENTOR. M. M. JOHNSON A TTORNE K5 EXHAUST GAS SMOKE DENSITY, BLACK A Sept. 25, 1962 Filed Feb. 9, 1959 M. M. JOHNSON 3,055,172

JET ENGINE COMBUSTION PROCESSES 4 Sheets-Sheet 2 COMPOSITION OF COOLANT -WEIGHT 100% WATER.

25% ETHYL ALCOHOL; 75%WATER.

Q 25% (38%ETHYL CARBITOL, 6296ETHYL cELLosoLvE) 75% WATER.

25% l,4-D|OXANE; 75% WATER.

25% PROPYLENE OXIDE; 75%wATER.

3 f I I 2 .JP-4 REFEREE y FUEL NORMAL HEPTANE FUEL l I l l l 0 0.02 0.04 0.06 0.08 0.10

COOLANT AIR WEIGHT RATIO INVENTOR.

M. M. JOHNSON A TTORNEYS FIG. 2

RADIANT ENERGY FLUX- BTU/FTZ/HR x|o M. M. JOHNSON JET ENGINE COMBUSTION PROCESSES Filed Feb. 9, 1959 4 Sheets-Sheet 3 COMPOSITION OF COOLANT-WEIGHT I 100% WATER 25 /o ETHYL ALCOHOL 75 WATER.

JP-4 REFEREE FUEL E 9O E I NORMAL L. HEPTANE FUEL 7 E 1o 4 V 60 I I V g l 1 Q COOLANT -AIR WEIGHT RATIO F/Q 4 INVENTOR.

M. M. JOHNSON Sept. 25, 1962 Filed Feb. 9, 1959 M. M. JOHNSON 4 Sheets-Sheet 4 WEIGHT l,4-D|OXANE IN MIXTURE OF WATER FIG. 5

INVENTOR.

M. M. JOHNSON A TTORIVEVS SPECIFIC THRu'sT POUNDS United States Patent 3,055,172 JET ENGINE COMBUSTION PROCESSES Marvin M. Johnson, Bartlesville, Okla, assignor to Phillips Petroleum Company, a corporation of Delaware Filed Feb. 9, 1959, Ser. No. 792,163 26 Claims. (Cl. 60-354) This invention relates to the operation of continuous combustion typepower plants. Inv one aspect this invention relates to the operation of jet engines. In another aspect this invention relates to reduction of the smoke density of exhaust gases from a jet engine. In still another aspect this invention relates to the augmentation of thrust in jet engines.

This application is a continuation in part of my copending application Serial No. 740,492, filed June 6, 1958, now abandoned.

in recent years jet engines have been employed in increasingiy large numbers for the purpose of propelling aircraft, particularly military aircraft, and have been found to be highly advantageous in high speed aircraft. In the last few years, said jet engines have been employed in propelling commercial aircraft. With the increase in use of such engines, however, a number of operational problems have been recognized.

Aircraft jet engines can be classified broadly into three general categories or types; turbo engines, e.g., turbo-jet and turbo-prop; ram jet; and pulse jet. The present invention is primarily applicable to the aircraft turbo engines, and is particularly applicable to turbo-jet engines. For this reason and for the sake of brevity the invention will be described herein primarily as applied to a turbojet engine.

A conventional turbo-jet engine comprises three main parts or sections. One of those sections is the compressor section. In the compressor section, kinetic energy is imparted to the air stream and is trans-formed in a diffuser into potential energy as measured by an increase in static pressure in the compressor. Said compressor can be either an axial or a centrifugal compressor. The second part or section, a combustor, is provided to receive compressed air and fuel which is burned therein to increase the temperature of said air and resulting combustion gases within the combos-tor. Said combustor can be any one of the conventional types, as for example, one that employs multiple combustion chambers (cans) or one that employs an annular combustion tube or chamber. In the can type, the air flow is split upon leaving the compressor section and equal portions are sent to each can, where said portions are combusted with portions of the fuel. The combustion products are then recombinedwith sec ondary air and routed to the turbine section. In the annular type of combustion chamber the primary portion of the air is diverted from the main stream and directed toward the fuel injector within said combustion chamber where it burns with the fuel. The remaining or secondary air is then mixed with the products of combustion at a point downstream from the point of introduction of said primary air. The third main part of the engine, the turbine section, is ordinarily provided downstream of the combustor section and receives combustion gases from the combustion chamber. The gas turbine unit in the turbine section receives the gases from the combustor and 80-90 percent of the power developed by said turbine is employed to drive said compressor and the various auxiliaries of the engine. The remaining power, together with the gases exhausted from said turbine, is available to propel the aircraft. Thus, forward thrust for the turbo-jet engine is provided by the high velocity jetof gases which emerges from the turbine. In a turbo-prop engine, said remaining power not utilized to drive the 2 compressor and various auxiliaries, is transmitted to and drives a propeller.

Performance of a turbo-jet engine is dependent to a large extent upon the temperature rise which is obtainable 'in the engine. Temperature rise is that increase in temperature between the inlet to the combustor and the temperature of the gases at the conibustor exhaust outlet. The temperature rise must be carefully controlled, however, for the operation of a turbo-jet engine is limited by the ability of the turbine blades to withstand high temperatures. Fuel which is supplied to the combustor is burned in the presence of suppled air and raises the temperature of the combustion gases and unused air by the heat of combustion. An excess of air is conventionally utilized to control the temperature of the gases contacting the turbine blades. The hot gases are expanded through the turbine section which provides power for the compressor as mentioned above. Further expansion takes place in a rearwardly extending exhaust nozzle to provide asubstantial increase in gas velocity. The thrust which is provided by the engine equals the gas mass flow to the exhaust duct times its increase in speed according to the law of momentum.

As mentioned above, the temperature rise which is obtained in the engine must be carefully controlled and is limited by the ability of the turbine blades to withstand high temperatures. This enforced control of temperature rise creates operational problems, particularly at takeolf under high load, and during emergency conditions in flight when an abnormally large increase in developed thrust is necessary. Generally speaking, approximately fifty percent more power or thrust is required at takeoff than is required under normal cruising conditions. This large amount of thrust required at takeoff, and the necessity for providing extra power or thrust for emergency conditions which occur in flight, has presented serious problems for engine designers and manufacturers. Obviously the greater load which can be lifted at takeolf renders operation of the aircraft more profitable in commercial operations and more elfective in military operations. Just as obvious, however, there is a point of economic balance as ,well as weight balance. In general, it is not economical or practical to equip an aircraft with excessively large engines, or an excessive number of enr gines, in order to be able to lift maximum load at takeoff and then employ a reduced number of said engines, or only about fifty' to sixty percent of the available power of the engines, at cruising speed.

To overcome this problem present day turbo-jet engines have been designed to operate with the injection of a power augmentation or thrust augmentation liquid at takeoff, and in emergency conditions which may develop in flight. These thrust augmentation liquids serve to lower the temperature of the gases exhausted from the combustion chamber before said gases enter the turbine section and thus make it possible to burn more fuel with out exceeding a maximum temperature for said exhaust gases. Thrust augmentation liquids such as water, and mixtures of methyl alcohol or ethyl alcohol with water, are conventionally injected into the compressor inlet or into the combustion chamber of a jet engine. Said thrust augmentation liquids can be injected into the air inlet upstream of the compressor, into the compressor itself, into the diffuser downstream of the compressor and upstream of the combustion chamber, or directly into the combustion chamber. As discussed hereinafter, it is usually preferred to inject the thrust augmentation liquid directly into the compressor. Regardless of the point of injection, said liquids by being vaporized extract heat and thus act to cool the gases entering the turbine section, thereby permitting more fuel than normal to be burned within the combustion section without exceeding the maximum temperature limits which can be tolerated within said turbine section. It has been found that a 24 percent increase in thrust can be realized with water injection in a centrifugal machine, but the increase is obtained at a very high specific liquid consumption. Water-alcohol injection tests on an axial flow compressor turbo-jet have shown an increase of 12-16 percent in thrust. The higher value was obtained with water injection at the compressor inlet, the lower value was obtained with water and alcohol injected into the combustion chamber.

While the prior art use of water and alcohol-water mixtures, such as ethyl alcohol-water mixtures, augments the thrust developed by the engine, the use of such liquids has created other problems and leaves much to be desired. The use of alcohol-water mixtures resultsin (1) relatively low combustion efiiciency and (2) excessive smoke and a general combustion dirtiness. Because of the low flame speed, or rate of flame propagation of alcohol-water mixtures, difficulties in flame stabilization and irregular temperature profiles across the inlet of the turbine are encountered. In addition, the amount of this mixture which can be added for thrust augmentation is limited by its combustion instability, i.e., the flame speed is too low, and hence the total thrust'gained in this manner is limited. In other Words, the maximum proportion of the air made available for combustion by the compressor. cannot be utilized for combustion. Alcohol also tends to permit exhaust of flame from the combustor into the turbine during takeoff and to burn with a smoky flame, resulting in an excessive amount of smoke in the exhaust gases from the aircraft. The problem of increased smoke in the exhaust gases, measured as an increase in smoke density, is serious; particularly in those localities afllicted with smog problems or fog problems. Indeed, the problem is so severe in some localities that local authorities have required that the smoke density be lowered to acceptable values or the operation of the jet aircraft be suspended. Furthermore, not only is a nuisance created insofar as the locality immediately surrounding the airport is concerned, the thick clouds of smoke which are ejected are a hazard to operation of the airport itself and to other planes operating in and out of the airport.

I have found that the cyclic ethers are excellent thrust augmentation liquids which accomplish at least three improvements in the operation of jet engines; said cyclic ethers (1) act as coolants for the gases exhausted from the combustion chamber and thus augment thrust by permitting more fuel to be burned in said combustion chamber; (2) decrease the smoke density of the gases exhausted from the engine; and (3) eliminate or mitigate the problem of flame exhaust from the combustor into the turbine. Thus, broadly speaking, my invention resides in a method of operation of an aircraft turbo engine which method comprises introducing an aqueous mixture comprising water and a cyclic ether into a combustion zone of said engine. Cyclic ethers containing from 1 to 3 oxygen atoms, from 2 to 4 carbon atoms, and from to 1 nitrogen atoms in the ring, and a total of from 2 to carbon atoms in the molecule, are particularly useful in the practice of the invention.

By the term thrust augmentation, augmentation of thrust, or to increase thrust, or the like, is meant increase in thrust obtained from use of a supplementary or auxiliary apparatus or operation over the thrust obtained without use of such supplementary or auxiliary apparatus or operation. For example, prior art teaches the addition of ethyl alcohol-water mixtures to conventional jet engine fuels to augment thrust of engines operating on conventional fuels. 1

By the term specific thrust is meant the pounds of force exerted on the craft per pound of air used in the combustion of the fuel.

An object of the invention is to provide an improved method of operating an aircraft turbo engine. Another turbo-jet aircraft.

object of the invention is to provide a method for reducing the smoke density of the gases exhausted from an aircraft turbo engine. Another object of the invention is to provide a method for augmenting the thrust developed by an aircraft turbo engine by introducing a thrust augmentation liquid comprising a cyclic ether into a combustion zone of said engine. Still another object of the invention is to provide an improved thrust augmentation mixture for use in aircraft turbo engines. Another object of the invention is to eliminate or mitigate the problem of wherein R and R can be alike or unlike and each is selected from the group of radicals consisting of and =CH-CH and and said radicals wherein at least one hydrogen atom attached to a carbon atom is replaced with an alkyl substituent containing from 1 to 6 carbon atoms and the total number of carbon atoms in said substituents does not exceed 6.

The invention will be further described as applied to However, it is to be understood that the invention has application to any type of aircraft turbo engine such as turbo-jet, turbo-prop, or turbo-prop-jet.

FIGURE 1 is a diagrammatic illustration of the functional portions of a turbo-jet engine.

FIGURE 2 is a graph showing the effect of various thrust augmentation mixtures (coolants) on the density of smoke in the exhaust gases resulting from the combustion of various hydrocarbon fuels.

FIGURE 3 is a graph showing the eifect of various thrust augmentation mixtures (coolants) on combustion efliciency.

FIGURE 4 is a graph showing the efiect of various thrust augmentation mixtures (coolants) on radiant energy flux.

In FIGURE 5, curve T illustrates maximum turbine inlet temperature in a jet engine as a function of the dioxane content of a mixed 1,4dioxane-water jet engine fuel; curve F illustrates the calculated specific thrust per pound of air as a function of the dioxane content of the mixed 1,4-dioxane-water fuel.

Examples of the cyclic ethers which can be employed in the practice of the invention include, among others, the following: ethylene oxide; propylene oxide; 2,3-epoxybutane; 1,2-epoxybutane; 2,3-epoxyhexane; furan; 2' methylfuran; Z-ethylfuran; B-n-propylfuran; 2-isopropylfuran; 2-hexylfuran; 2,3-dimethylfuran; 2,4-dimethylfuran; 2,5-dimethylfuran; 2-methyl-3-ethylfuran; 2- methyl-S-ethylfuran; 2-ethyl-3-methylfuran; 2-ethyl-3- methylfuran; tetrahydrofuran; Z-methyltetrahydrofuran; 3-ethyltetrahydrofuran; 2-isopropyltetrahydrofuran; 2- butyltetrahydrofuran; Z-hexyltetrahydrofuran; 2,3 -dimethyltetrahydrofuran; 2,4-dimethyltetrahydrofuran; 2- methyl-3-ethyltetrahydrofuran; 2 methyl-S-ethyltetrahydrofuran; s-trioxane; methyl-s-trioxane; n-propyl-s-trioxane; 2,4-dimethyl-s-trioxane; 2-methyl-4-ethyl-s-trioxane; 1,4-dioxane; methyl-p-dioxane; ethyl-p-dioxane; propyl-pdioxane; hexyl-p-dioxane; 2-methyl-3-ethyl-p-dioxane; 2- methyl-S-ethyl-p-dioxane; 2-methyl-6-ethyl-p-dioxane; 1,3 dioxane; Z-methyl-m-dioxane; 4-ethyl-m-dioxane; 5- propyl-m-dioxane; Z-hexyl-m-dioxane; Z-rnethyl-S-ethylm-dioxane; 2-ethyl-4-methyl-m-dioxane; morpholine; 2- methylmorpholine; S-ethylmorpholine; Z-butylmorpholine; 6-hexylmorpholine; 2-methyl-3-ethylmorpholine; 3- methyl-Z-ethylmorpholine; pentoxazolidine; 4 methylpentoxazolidine; 2-ethylpentoxazolidine; S-n-propylpentoxazolidine; 6-butylpentoxazolidine; 2-methyl-4-ethylpentoxazolidine; 2-ethyl-S-methylpentoxazolidine; oxazolidine; 2-methyloxazolidine; 5-isopropyloxazolidine; 4- n-hexyloxazolidine; 2-methyl-4-ethyloxazolidine; and 4- methyl-S-ethyloxazolidine.

The cyclic ethers of the invention are usedin admixture with water, e.g., an aqueous solution or an aqueous emulsion. Said aqueous solution or aqueous emulsion ordinarily can contain from about 10 to about 90 weight percent of cyclic ether, preferably to 35 weight percent of cyclic ether, based on the total mixture. The majority of said cyclic ethers are completely miscible with water and the thrust augmentation liquid is prepared by simply mixing said cyclic ether with water in the desired amount.

However, in some instances, the cyclic ethers are not completely miscible with water; for example, the furans.

In such instances, it is necessary to employ an emulsifying agent and form a stable emulsion of the cyclic ether with water. Any suitable emulsifying agent which will form a stable emulsion can be used. However, the preferred emulsifying agents are those which leave no ash in the combustion chamber, i.e., those which will be completely burned in said combustion chamber. Examples of such ashless emulsifying agents are polyoxyethylene sorbitan monolaurate, sorbitan monolaurate, a mixture of 55 percent of said polyoxyethylene sorbitan monolaurate and 45 percent of said sorbitan monolaurate, and others. The amount of the emulsifying agent employedwill obviously depend upon the material to be put into emulsion with water. Generally speaking, amounts up to about 1 percent are employed.

In the practice of the invention, the thrust augmentation liquid (coolant) can be injected into (a) the air inlet to the compressor, (b) directly into the compressor, (c) the diffuser, i.e., downstream of the compressor and up-, stream'of the combustion chamber, (d) or directly into the combustion chamber. Of these possible points of injection of the thrust augmentation liquid, injection into the inlet of the compressor is usually the least preferred because injection at this point reduces the capacity of the compressor. Injection directly into the compressor is the most preferred point of injection for the thrust augmentation liquid. When injected into the compressor, said liquid is introduced at some intermediate stage of compression, preferably at a point where favorable intercooling occurs. Introduction of the thrust augmentation liquid directly into the compressor is preferred because when so injected said liquid cools the air as it is being compressed and thus acts as an intercooler in said compressor, greatly increasing the capacity of said compressor. As will be understood by those skilled in the art, an increase in the capacity of the compressor will ultimately result in more available thrust from the engine because more air, at a lower temperature, is available to permit the burning of more fuel in the combustion chamber.

The advantages of the invention can also be realized by injection of the thrust augmentation liquid into the diffuser downstream of the compressor or directly into the combustion chamber because introduction at these two points will also result in cooler exhaust gases from said combustion chamber for introduction into the turbine section. However, since the thrust augmentation liquid is introduced downstream of the compressor, the advantage of the increased capacity of the compressor as discussed above is sacrificed. For these reasons, the latter two points of introduction are less preferred than injection of the thrust augmentation liquid directly into the compressor.

Regardless of the place of injection of the thrust augmentatiqn liquid, the cyclic ethers of the invention are ultimately introduced into the combustion chamber, the exhaust gases from said combustion chamber are cooled; and the smoke density of said exhaust gases is caused to be decreased. In the practice of the invention the thrust augmentation liquid is introduced into said combustion chamber in an amount sufiicient to appreciably augment the thrust of the engine and/or sufficient to appreciably reduce the smoke density of the exhaust gases from said engine. The actual amount of thrust augmentation liquid introduced into said combustion chamber will vary depending upon the design of the specific engine, operating conditions such as the altitude at which theengine is operating, the load carried by the aircraft the engine is propelling, and other factors as will be understood by those skilled in the art. Therefore the invention is not limited to the introduction of any specific amount of the thrust augmentation liquids (coolants) of the invention. Said thrust augmentation liquids (coolants) are usually introduced in an amount sufficient to give a coolant to air weight ratio within the range of about 0.001 to about 0.15. In many instances it is preferred that said ratio be in the range of about 0.001 to about 0.10 or lower such as from 0.001 to about 0.07. However, with some engines under some conditions said ratio can go as high as 0.2 or higher. When the thrust augmentation liquid (coolant) is introduced directly into the primary combustion portion of the combustion chamber it'is preferably introduced in an amount suflicient to give'a coolant to air weight ratio within the lower portion of said range, e.g., from about 0.001 to about 0.10. It is within the scope of the invention to inject a portion of the thrust augmentation liquid into the primary portion of the combustion chamber and another portion into the secondary portion of said combustion chamber. Thus, a suitable overall range of injected thrust augmentation liquid is an amount sufficient to give a thrust augmentation liquid to air ratio within the range of about 0.001- to about 0.2.

Referring to FIGURE 1 of the drawings the invention will be more fully explained. Since the operating cycle and the elements of a conventional turbojet engine are well known to those skilled in the art, the functional parts of a turbo-jet engine have been illustrated diagrammatically. In FIGURE 1, there is illustrated a compressor means 11 having an air inlet means 10 for the introduction of air into said compressor means. In said compressor the air is usually compressed to a pressure within the range of about 4 to 12 atmospheres. From the compressor, the compressed air flows into combustion section 12 where it is combined with a metered, and atomized or prevaporized, amount of fuel and its temperature increased by combustion of said fuel. From said combustion section 12 the exhaust gases comprising combustion products and excess air flow to turbine 13 which may contain one or more turbine rotors and one or more stages. Said gases entering said turbine section cause the turbine rotor or rotors to revolve and to drive the compressor in said compression section by means of shaft means 15 which connects the compressor in said compression section and the turbine in said turbine section. The gases exhausted from said turbine section then flow through tail pipe section 14 and are vented to the atmosphere through exhaust nozzle 16.

In the practice of the invention, the thrust augmentation liquid (coolant) comprising one or more of the cyclic ethers of the invention can be introduced into the inlet of the compression section 11 by means of conduit 17; directly into the compressor in said compression section by means of conduit 18; into the diffuser downstream of said compression section and upstream of said combustion section 12 by means of conduit 19; or directly into said combustion section 12 by means of conduit 21. As explained hereinafter, when, according to another feature of the invention, the cyclic ether-water mixtures of the invention are employed as the primary fuel in the jet engine or as fuel in the afterburner section, said mixture is introduced through conduit 22 or conduit 23 instead of the normally used hydrocarbon fuel. Any suitable conduit means and injection means can be employed for injecting the cyclic ether-water mixtures at the above mentioned places.

The following examples will serve to further illustrate the invention.

EXAMPLE Two series of test runs were carried out in a 2-inch diameter fuel atomizing combustor embodying features common to full scale turbo-jet combustion systems. Said combustor comprises a perforated flame tube closed at its upstream end and mounted within an outer shell to provide an annular air flow space between said flame tube and said shell. Said annular air flow space is closed at its downstream end so as to cause air to enter said flame tube through said perforations. The ratio of primary combustion air to secondary quench or diluent air is about 1 to 4, based on the area of the perforations in the upstream and downstream portions of said flame tube. Fuel is injected into said flame tube through an atomizing nozzle axially positioned in the upstream end thereof. Some air is admitted around the fuel spray nozzle in a swirling pattern. to assist atomization of the fuel.

In one series of test runs the primary fuel used was a JP-4 referee fuel having the properties set forth in Table I below. In the other series of test runs the primary fuel used was normal heptane. various thrust augmentation liquids (coolants) to be tested were injected at various coolant to air weight ratios into the air stream downstream from the compressor and upstream from said combustor a suflicient distance to permit complete vaporization of said liquid prior to entry into said combustor.

Average operating conditions of the combustor during each of said test runs were as follows:

Inlet air pressure 300 inches Hg Abs. Inlet air velocity 100 feet per second. Inlet air temperature 600 F.

Exhaust gas temperature 1300 F.

Said exhaust gas temperature was maintained essentially constant at 1300 F. for each test run by varying the fuel to air weight ratio within the limits of 0.0117 to 0.0161 to compensate for the amount of coolant injected.

During said test runs the following were determined: smoke density of combustor exhaust gases; combustion efiiciency; and radiantfenergy flux. The results of these determinations are shown graphically in FIGURES 2, 3, and 4. Said smoke density measurements were made with an E. K. Von Brand continuous gas sampling and filtering recorder. The filter paper strips from said Von Brand In both series .of test runs the p recorder were evaluated with a Welch Densichron reflection head densitometer which rated said strips between 0 and 100 according to blackness. Said combustion efficiencies were calculated from the inlet air temperature, the exhaust gases temperature, and the heats of combustion of the injected hydrocarbon fuel and coolant. Said radiant energy flux measurements were made with Leeds and Northrup Rayotube thermopile pick-ups positioned so as to see the flame through perforations in the primary combustion section of the flame tube and through sapphire windows in the outer shell surrounding said flame tube.

Some of the properties of the minimum quality JP-4 Referee fuel used as the primary fuel in a portion of the above described test runs are given in Table I below. Said fuel conformed with JP-4 specifications in every respect.

TABLE I Properties of JP-4 Referee Fuel API gravity 49.0 ASTM distillation, F.:

IBP 141 10% 224 50% 376 465 EP 514 Paraffins+naphthenes-LV percent 78.1 Aromatics-LV percent 19.6 OlefinsLV percent 2.3

A comparison of the results given in FIGURE 2 shows that the smoke density of the combustor exhaust gases was markedly less when a cyclic ether was a component of the thrust augmentation liquid (coolant) (see curves 4 and 5) than was the case with the prior art thrust augmentation liquids (see curves 1 and 2). A comparison of curves 4 and 5 with curve 3 shows that the cyclic ethers are much more effective than the straight chain ethers in suppressing smoke.

A comparison of the results shown in FIGURE 3 shows that the combustion efliciency is higher throughout the preferred operating range of coolant injection when a cyclic ether such as 1,4-dioxane (curve 4) or propylene oxide (curve 5) was a component of the thrust augmentation liquid (coolant), than when the prior art thrust augmentation liquid ethyl alcohol-water (curve 2) was used. Higher combustion efficiencies are of course desirable.

A comparison of the results shown in FIGURE 4 shows that the radiant energy flux was markedly less when a cyclic ether such as 1,4-dioxane (curve 4) or propylene oxide (curve 5) was a component of the thrust augmentation liquid (coolant), than when the prior art thrust augmentation liquids ethyl alcohol-water (curve 2) or water only (curve 1) were used. Lower values of radiant energy flux are much desired because fewer hot spots develop and less corrosion occurs.

Any suitable type of hydrocarbon fuel can be employed in the practice of the invention. Said fuels which can be so employed include the conventional jet engine fuels which comprise a blend of hydrocarbons boiling in the range from about to about 700 R, such as gas oils, kerosene, and gasolines, including aviation gasoline. Fuels of the paraffin and naphthenic type having relatively low aromatic content, i.e., not more than about 20 liquid volume percent aromatics, as well as fuels of the aromatic type having high aromatic contents ranging from about 20 up to about 88 percent or higher liquid volume percent aromatics, can be employed in operating continuous combustion turbo type aircraft engines according to the practice of the invention. Hydrocarbon fuels 7 having wide boiling range, such as JP-3, JP-4, or fuels of the kerosene type, such as JP-S, can be employed, the

9 boiling range of these fuels generally being in the range of about 200 to about 600 F.

Hydrocarbon fuel and air are injected into the corn bustion zone of jet engines at a fuel to air weight ratio between 0.005 to 0.10. Turbo-jet engines are preferably operated on an overall fuel to air weight ratio between 0.01 and 0.03. In the practice of this invention, hydrocarbon fuel and air are injected into the combustion zone of the engine at a fuel to air weight ratio between 0.005 to 0.10. The exact fuel to air ratio which is utilized will depend upon engine design limitations, such as turbine durability and the like, aswill be understood by those skilled in the art. The air supplied to the turbo-jet engine will generally have an air inlet pressure between about 40 and about 500 inches of mercury absolute and will have a linear air velocity of from about 30 to about 200 feet per second. The fuel supply to the combustor will have a temperature of between about 60 F. and about 350 F. The air is usually supplied to the combustor at a temperature between about 30 F. and about 900 F., more frequently between 100 F. and 760 F. Fuel injection temperature will be dependent upon fuel characteristics such as freezing point and volatility as well as injection nozzle characteristics.

As an added feature of the invention, the cyclic etherwater mixtures of the invention, i.e., either aqueous solutions or aqueous emulsions, can be utilized as the primary fuel in the operation of the jet engine instead of a conventional hydrocarbon fuel. Said cyclic ethers have been found to have superior flame speeds which make them particularly suitable for use as primary fuels in jet engines. Said cyclic ether-water mixtures are particularly suitable for use in engines where it is necessary that the combustion gas mixture exhausted from the combustor be a non-oxidizing mixture, for example when the turbine is provided with molybdenum-containing blades. The following Table II lists some properties of some of the above-mentioned cyclic ethers, and also includes isopropyl ether, diethyl ether, methyl alcohol, ethyl alcohol, normal It is to be noted from the data given in the above Table III that under the conditions there given, combustion of the cyclic ether-s was stable to very stable. Said cyclic ethers possess exceptionally high flame speeds, as given above.

In operating a turbo aircraft engine provided with molybdenum containing turbine blades at 3,000 R., it is necessary that the combustion gas mixture exhausted from the conrbustor and fed into the turbine be a nonoxidizing mixture. A nonoxidizing combustion gas mixture at 3,000 R. in an open cycle jet engine or gas turbine can be obtained by burning an over-rich combustion mixture, as for example, 3 /2 to 4 times the stoichiometric proportion of fuel to air. A second method for preventing rapid deterioration of molybdenum containing turbine blades or other parts is to use, at stoichiometric ratio, certain fuels and air with added 'water to provide a heat sink. Sufficient water is added to the fuel to lower the temperature of combustion to a level below that at which molybdenum containing parts are rapidly oxidized. I have found that water mixtures of the above-disclosed cyclic ethers serve well as gas turbine engine fuels in the protection of molybdenum containing blades in the heptane, and JP-4 fuel for comparison purposes. 9 turbine.

TABLE II Density Flame M.P. C. B.P. C 20l4 speed, Solubility in water cm./sec.

1,3-dioxane (meta) -42" F. 105-6 1. 034 62 In all proportions. lA-dloxune (para)- 9. 5-10. 5 101. 1 1.033 62 Do. Ethylene oxide 1ll 10. 5 0. 897 70 D0. Propylene o\ide 35 0. 859 63 33 g./100 cc. Furan 31. 3 0. 944 Insoluble. Isopropyl ether. 67. 5 0. 726 41 0.2 g./100 cc. Diethyl other ll6 34. 5 0. 708 37 7.4 g./l00 cc. Methyl alcoho -97 64. 5 0.786 46 83 .3 g./l00 cc. Ethyl alcohol- 112 78. 4 0. 789 41 In all proportions. JP-4 (jet engine fuel) About 43 Insoluble.

l Laminar flame speed of air at a fuelzair ratio and H20).

From the above-listed flame speed values it is to be noted that the cyclic ethers have high flame speeds compared to the flame speeds of the other materials given in Table II. The cyclic ethers also exhibit high combustion efiiciencies, In general, the cyclic ethers possess such anti-freeze qualities that they can be used or stored in cold climates.

Another important advantage of the above-disclosed cyclic ethers when used as fuels in jet engines is their high combustion stability under such severe operating conditions as takeoff from the ground under full load, or emergency conditions which occur in flight. The data given in the following Table III illustrate the stability of combustion when burning aqueous mixtures of some of the above-disclosed cyclic ethers under different temperature and pressure conditions:

in water vapor-air mixtures containing 0.25 pound water per pound of .80 percent of stoichioinetric or complete combustion of 00 tion of the mass rate of flow of air and fuel and of the.

difference between the velocity of the jet and the craft being propelled thereby, as indicated by the following formula:

I l in which G==mass rate of flow of air and fuel, as in pounds per second; g=the acceleration due to gravity in feet per second; V =velocity of the jet in feet per second and V=the velocity of the craft, also in feet per second.

1?. mixture. The greater the dioxane content the higher is the combustion temperature.

The following Table IV gives exemplary temperatures at the inlet and outlet of the turbine, the mass rate of flow of air and fuel, and the exhaust nozzle pressures 3 given flight speed the thrust of the engine can 5 when using various 1,4-dioxane-water mixtures as the pribe increased by increasing V,, the velocity of the jet, or mar-y fuel.

TABLE IV Tempera- Weight per- Mass rate tureinqrease Turbine Turbine Nozzle Nozzle Specific cent dioxane of flow of 1 through inlet; outlet pressure, outlet thrust,

in 1,4-dloxpound air combustion temp. temp. atmostempcra- (lbs. force/ ane-water iuel chamber R. B. pheres ture, R. lb. air/sec.)

mixtures R.

60. 1. 202 2, 800 a, 000 3, 554 7. 41 2, 345 174. 3 50. 0 1 243 2,600 a, 700 3,365 7. 37 2, 220 174 33. a 1. 364 2, 010 3, 110 2, 803 6. 94 1, 870 173 2a. 6 1. 429 1, 745 2, 845 2, 554 6.81 1, 712 172 25. 0 1, 486 1, 515 2, 615 2, 333 6. 69 1, 580 169 20. 0 1. 607 1,100 2, 200 1, 941 6. 32 1, 312 167 15. 0 1.850 428 1, 528 1, 203 3. 50 925 40.

by increasing G, the mass rate of flow of the air and fuel, The specific thrust values in the above tabulation were or both V and G. used in plotting curve F in FIGURE 5; and the temper- With the use of the cyclic ether-water mixtures of the atures (in F.) were used in plotting curve T of FIG- invention, the value of G for a given turbine inlet tem- URE 5. perature is increased, thereby increasing engine thrust. While certain embodiments of the invention have been The temperature of combustion of the cyclic ethers is described for illustrative purposes, the invention obviusually too high to permit their use per se as primary ously is not limited thereto. fuels. For example, 1,4-dioxane and 1,3-dioxane possess I claim: combustion temperatures of about 3800 F.; temperatures 1. In the method of operating an aircraft turbo engine too high for available metals from which turbine blades wherein air and a fuel are burned in a combustion zone etc. are made. Thus the temperature of combustion of of said engine and resulting gases are exhausted from the dioxanes must be tempered as by a heat sink, i.e., said engine so as to impart thrust thereto, the step of inaddition of water. troducing into said combustion zone an aqueous mixture When the cyclic ether-water mixtures of the invention comprising from 10 to 90 weight percent of water and are utilized as a primary fuel (instead of a conventional from 90 to 10 weight percent of a cyclic ether containing hydrocarbon fuel) in an aircraft turbo engine the cyclic from 1 to 3 oxygen atoms and from 2 to 4 carbon atoms ether content of said mixtures is preferably within the in the ring, and a total of from 2 to 10 carbon atoms in range of about to 60 weight percent. When said cyclic 40 the molecule. ether is a dioxane, such as 1,4-dioxane, amixture of about 2. The method of claim 1 wherein said cyclic ether 50 weight percent dioxane has been found quite practical. contains: from 1 to 3 oxygen atoms, from 2 to 4 carbon It is also within the scope of the invention to inject atoms, and 1 nitrogen atom in the ring; and a total of the cyclic ether-water mixtures of the invention into the from 2 to 10 carbon atoms in the molecule. afterburner section of the jet engine. When so utilized 3. In the method of operating an aircraft turbo engine the cyclic ether content of said mixtures can be from wherein air and a hydrocarbon fuel are burned in a cornabout 10 to about 90 weight percent, preferably from bustion zone of said engine and resulting gases are exabout 15 to about 35 weight percent, based on the total hausted from said engine so as to impart thrust thereto, mixture. When said cyclic ether is a dioxane, such as the step of introducing into said combustion zone, sepa- L all aqueous mixture Containing from 20 0 25 rately from said fuel, an aqueous mixture comprising from weight percent dioxane has been found quite practical. 10 t 90 i h percent f water d fro 90 to 10 Obviously said cyclic ether-water mixtures would be inweight percent of a cyclic ether having a structural forjected into said after burner section in an amount sufiimula selected from the group consisting of cient to appreciably augment the thrust of the engine. Rid! As stated above, the cyclic-ether content of the aqueous mixtures of the invention can vary from about 10 to about i O 90 weight percent, preferably l535 weight percent, of the and total mixture. When said cyclic ether is a dioxane, such X as 1,4-dioxane, a dioxane content of about 20 to about weight percent of the total mixture has been found quite so 0 satisfactor for said mixtures.

The foll owing gives exemplary operating conditions of wherem' R1 and R2 can be ailke and l i and each 18 the apparatus of FIGURE 1 from the air inlet to the exselected from the group of radicals conslstmg of h =CH -CH and =CHCH CH and X is selected aust nozzle. f

rorn the group of rad1cals consisting of Combus -CH=CH-CH=CH Compressor Compressor tion CHQ CH2 CH, CH,

inlet outlet clgalrtrigter CE-CHPO-H, CH2CH2CH-OCH: aaiaaar affr 52%. w Mass of air, pounds.. 1 1

-CHr-'GH2N-CHCH:- The temperature of the gases leaving the combustion Y chamber will, of course, vary with the fuel composition, e.g., with the proportion of dioxane in the dioxane-water 'CHPCHPCHPNL'CHP and said radicals wherein at least one hydrogen atom attached to a carbon atom is replaced with an alkyl subi stituent containing from 1 to 6 carbon atoms and the total number of carbon atoms in said substituents does not exceed 6.

4. In the method of operating a turbo aircraft engine wherein air is introduced into and compressed in a com pressor, the resulting compressed air is introduced into a combustion chamber of said engine, a hydrocarbon fuel is introduced into said combustion chamber and burned with a portion of'said air to form a mixture of combustion gases and air, said mixture is exhausted from said com-bustion chamber through a turbine and out of a rearwa-rdly extending exhaust duct to impart thrust to said engine, the improvement which comprises introducing into said combustion chamber, separately from said fuel, as a thrust augmentation liquid an aqueous mixture comprising from 10 to 90 weight percent of water and from 90 to 10 weight percent of a cyclic ether as defined in claim 3.

5. The method of claim 4 wherein said aqueous mixture is injected into the inlet of said compressor, along with said air, and passes to said combustion chamber along with said air.

6. The method of claim 4 wherein said aqueous mixture is injected into an intermediate stage of said compressor and passes to said combustion chamber along with said air.

7. The method of claim 4 wherein said aqueous mixture is injected into said compressed air stream downstream from said compressor but upstream of said combustion chamber and passes to said combustion chamber along with said air.

8. The method of claim 4 wherein said aqueous mixture is injected directed into said combustion chamber.

9. In the operation of a turbo aircraft engine wherein a hydrocarbon fuel and air are burned in a combustion zone of said engine, a thrust augmentation liquid is in troduced into said combustion zone, and resulting gases are exhausted from said engine so as to impart thrust thereto, the method of reducing the smoke density of said exhaust .gases which comprises introducing into said combustion chamber, separately from said fuel, as said thrust augmentation liquid an aqueous mixture comprising from 10 to 90 weight percent water and from 90 to 10 weight percent of a cyclic ether as defined in claim 4.

10. The method of claim 4 wherein said aqueous mixture is introduced into said combustion chamber in a thrust augmentation liquid to air weight ratio within the range of 0.001 to 0.2.

11. The method of claim 4 wherein said aqueous mixture comprises from 85 to 65 weight percent of water and from to 35 weight percent of a cyclic ether as defined in claim 4.

12. The method of claim 4 wherein said aqueous mixture comprises from 80 to 40 weight percent water and from 20 to weight percent of a dioxane.

13. In the method of operating a turbo aircraft engine wherein a hydrocarbon fuel and air are burned in the combustion chamber of said engine to form a mixture of combustion gases and air, said mixture is exhausted from said combustion chamber through a turbine, gases from said turbine are passed through an aftenburner section of said engine and then exhausted through an exhaust duct so as to impart thrust to said engine, the improved method of augmenting'the thrust of said engine and reducing the smoke density of said exhaust gases therefrom, which comprises introducing into said combustion chamber, separately from said fuel, an aqueous mixture comprising from 10 to 90 weight percent of water and from 90 to 10 weight percent of a cyclic ether as defined in claim 4. v

14. The method of claim 13 wherein said aqueous mixture comprises from 85 to weight percent water and from 15 to 35 weight percent of said cyclic ether, and is introduced into said main combustion chamber in an aqueous mixture to air weight ratio within the range of 0.001 to 0.15.

15. The method of claim 14 wherein said aqueous mixture comprises from to 40 weight percent of water and from 20 to 60 weight percent of a dioxane.

16. The method of claim 3 wherein said cyclic ether is 1,4-dioxane.

17. The method of claim 3 wherein said cyclic ether is 1,3-dioxane. 1

18. The method of claim 3 wherein said cyclic ether is ethylene oxide.

19. The method of claim 3 wherein said cyclic ether is propylene oxide.

20. The method of claim 3 wherein said cyclic ether is butylene oxide.

21. The method of claim 3 wherein said cyclic ether is furan.

22. The method of claim 3 wherein said cyclic ether is tetrahydrofuran.

23. The method of claim 3 wherein said cyclic ether is morpholine.

24.The method of claim 3 wherein said cyclic ether is trioxane.

25. The method of claim 3 wherein said cyclic ether is pentoxazolidine.

26. The method of claim 3 wherein said cyclic ether is oxazolidine.

References Cited in the file of this patent UNITED STATES PATENTS 2,551,229 Alford et al. May 1, 1951 2,563,305 'Bn't-ton et a1. Aug. 7, 1951 2,782,592 Koltenback et al Feb. 26, 1957 OTHER REFERENCES Mullens: Fuel, vol. 32, No. 3 (1953.), pp. 327-343.

Mullens: Fuel, vol. 32, No. 4 (1953), pp. 457-79.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,055,172 September 25, 1962 Marvin Mo Johnson It is hereby certified that error appears in the above numbered patent requiring correction and thet the said Letters Patent should read as corrected below.

Column 13 line 39, for "directed" read directly same column 13 lines 50 and 58, and column 14, line 17, for the claim reference numeral "4", each occurrence, read Signed and sealed this 26th day of March 1963,

(SEAL) Attest:

ESTON e. JOHNSON DAVID L. LADD Attesting Officer Commissioner of Patents UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,055,172

September 25, 1962 Marvin M, Johnson It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 13, line 39, for "directed" read directly same column 13, lines 50 and 58, and column 14, line 17,

for the claim reference numeral "4", each occurrence, read 3 Signed and sealed this 26th day of March 1963,

(SEAL) Attest:

ESTON G, JOHNSON Attesting Officer DAVID L. LADD Commissioner of Patents 

1. IN THE METHOD OF OPERATING AN AIRCRAFT TURBO ENGINE WHEREIN AIR AND A FUEL ARE BURNED IN A COMBINATION ZONE OF SAID ENGINE AND RESULTING GASES ARE EXHAUSTED FROM SAID ENGINE SO AS TO IMPART THRUST THERETO, THE STEP OF INTRODUCING INTO SAID COMBUSTION ZONE AN AQUEOUS MIXTURE COMPRISING FROM 10 TO 90 WEIGHT PERCENT OF WATER, AND FROM 90 TO 10 WEIGHT PERCENT OF A CYCLIC ETHER CONTAINING FROM 1 TO 3 OXYGEN ATOMS AND FROM 2 TO 4 CARBON ATOMS IN THE RING, AND A TOTAL OF FROM 2 TO 10 CARBON ATOMS IN THE MOLECULE. 